Compact Disc

Compact disc
Compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips
Philips and Sony
Sony and released in 1982. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. The first commercially available Audio CD player, the Sony
Sony CDP-101, was released October 1982 in Japan. Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to about 80 minutes of uncompressed audio or about 700 MiB of data. The Mini CD
Mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to 3.1 in); they are sometimes used for CD singles, storing up to 24 minutes of audio, or delivering device drivers. At the time of the technology's introduction in 1982, a CD could store much more data than a personal computer hard drive, which would typically hold 10 MB. By 2010, hard drives commonly offered as much storage space as a thousand CDs, while their prices had plummeted to commodity level. In 2004, worldwide sales of audio CDs, CD-ROMs and CD-Rs reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.[1] From the early 2000s CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U.S. had dropped about 50% from their peak; however, they remained one of the primary distribution methods for the music industry.[2] In 2014, revenues from digital music services matched those from physical format sales for the first time.[3]

Contents

1 History

1.1 Digital audio
Digital audio laser-disc prototypes 1.2 Collaboration and standardization 1.3 Initial launch and adoption 1.4 Further development and decline 1.5 Awards and accolades

2 Physical details

2.1 Integrity 2.2 Disc shapes and diameters

3 Logical format

3.1 Audio CD 3.2 Super Audio CD 3.3 CD-MIDI 3.4 CD-ROM 3.5 Video CD
Video CD (VCD) 3.6 Super Video CD 3.7 Photo CD 3.8 CD-i 3.9 CD-i Ready 3.10 Enhanced Music CD
Enhanced Music CD (CD+) 3.11 Vinyl Disc

4 Manufacture 5 Writable compact discs

5.1 Recordable CD 5.2 ReWritable CD

5.2.1 Speed

6 Copy protection 7 See also 8 References 9 Further reading 10 External links

History[edit] American inventor James T. Russell has been credited with inventing the first system to record digital information on an optical transparent foil that is lit from behind by a high-power halogen lamp.[4][5] Russell's patent application was first filed in 1966, and he was granted a patent in 1970. Following litigation, Sony
Sony and Philips
Philips licensed Russell's patents (then held by a Canadian company, Optical Recording Corp.) in the 1980s.[6][7][8] The compact disc is an evolution of LaserDisc
LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Philips
Philips and Sony
Sony independently in the late 1970s.[9] Although originally dismissed by Philips
Philips Research management as a trivial pursuit,[10] the CD became the primary focus for Philips
Philips as the LaserDisc
LaserDisc format struggled.[11] In 1979, Sony
Sony and Philips
Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red
Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984.[12] By 1988, CD sales in the United States surpassed those of vinyl LPs, and by 1992 CD sales surpassed those of prerecorded music cassette tapes.[13][14] The success of the compact disc has been credited to the cooperation between Philips
Philips and Sony, which together agreed upon and developed compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.[15] Digital audio
Digital audio laser-disc prototypes[edit] In 1974, L. Ottens, director of the audio division of Philips, started a small group with the aim to develop an analog[16] optical audio disc with a diameter of 20 cm (7.9 in) and a sound quality superior to that of the vinyl record.[17] However, due to the unsatisfactory performance of the analog format, two Philips
Philips research engineers recommended a digital format in March 1974.[16] In 1977, Philips
Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at 11.5 cm, the diagonal of an audio cassette.[16][18] Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization NHK
NHK in 1970, became general manager of Sony's audio department in 1971. His team developed a digital PCM adaptor
PCM adaptor audio tape recorder using a Betamax
Betamax video recorder in 1973. After this, in 1974 the leap to storing digital audio on an optical disc was easily made.[19] Sony
Sony first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony
Sony showed the press a 30 cm disc that could play 60 minutes of digital audio (44,100 Hz sampling rate and 16-bit resolution) using MFM modulation.[20] In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved error correction code—specifications similar to those later settled upon for the standard compact disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels.[20] Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips
Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called " Philips
Philips Introduce Compact Disc"[21] in Eindhoven, Netherlands.[22] Collaboration and standardization[edit]

Dutch inventor and Philips
Philips chief engineer Kees Schouhamer Immink
Kees Schouhamer Immink was part of the team that produced the standard compact disc in 1980

Sony
Sony executive Norio Ohga, later CEO and chairman of Sony, and Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism.[23] As a result, in 1979, Sony
Sony and Philips
Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology.[21] After a year of experimentation and discussion, the task force produced the Red
Red Book CD-DA
CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996. Philips
Philips coined the term compact disc in line with another audio product, the Compact Cassette,[18] and contributed the general manufacturing process, based on video LaserDisc
LaserDisc technology. Philips also contributed eight-to-fourteen modulation (EFM), which offers a certain resilience to defects such as scratches and fingerprints, while Sony
Sony contributed the error-correction method, CIRC. The Compact Disc Story,[16] told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around four to eight persons,[10][24] though according to Philips, the compact disc was "invented collectively by a large group of people working as a team."[25] Initial launch and adoption[edit] Philips
Philips established the Polydor Pressing Operations plant in Langenhagen
Langenhagen near Hannover, Germany, and quickly passed a series of milestones.

The first test pressing was of a recording of Richard Strauss's Eine Alpensinfonie (An Alpine Symphony) played by the Berlin Philharmonic and conducted by Herbert von Karajan, who had been enlisted as an ambassador for the format in 1979.[26] The first public demonstration was on the BBC
BBC television programme Tomorrow's World in 1981, when the Bee Gees' album Living Eyes (1981) was played.[27] The first commercial compact disc was produced on 17 August 1982. It was The Visitors (1981) by ABBA.[28] The first 50 titles were released in Japan
Japan on 1 October 1982,[29] the very first of which was a rerelease of the Billy Joel
Billy Joel album 52nd Street.[30] The first CD played on BBC
BBC Radio
Radio was in October 1982 on BBC
BBC Radio Scotland (Jimmy Mack programme, Followed by Ken Bruce and Eddie Mair all BBC
BBC Scotland), with the first CD played on UK independent radio station shortly after ( Radio
Radio Forth, Jay Crawford Show). The CD was Dire Straits, Love over Gold. [31]

The Japanese launch was followed in March 1983 by the introduction of CD players and discs to Europe[32] and North America (where CBS Records released sixteen titles).[33] This 1983 event is often seen as the "Big Bang"[by whom?] of the digital audio revolution. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities, and its handling quality received particular praise. As the price of players gradually came down, and with the introduction of the portable Discman the CD began to gain popularity in the larger popular and rock music markets. One of the first CD markets was devoted to reissuing popular music whose commercial potential was already proven. An advantage of the format was the ability to produce and market boxed sets and multi-volume collections.[11] The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms.[34] The first major artist to have his entire catalogue converted to CD was David Bowie, whose 15 studio albums were made available by RCA Records
RCA Records in February 1985, along with four greatest hits albums.[35] On February 26, 1987, the first four UK albums by The Beatles were released in mono on compact disc.[36] In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.[37] Further development and decline[edit]

Sony
Sony CD Walkman D-E330

The CD was planned to be the successor of the vinyl record for playing music, rather than primarily as a data storage medium. From its origins as a musical format, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Braat presented the first experiments with erasable compact discs during the 73rd AES Convention.[38] In June 1985, the computer-readable CD-ROM
CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony
Sony and Philips.[39] Recordable CDs were a new alternative to tape for recording music and copying music albums without defects introduced in compression used in other digital recording methods. Other newer video formats such as DVD
DVD and Blu-ray
Blu-ray use the same physical geometry as CD, and most DVD
DVD and Blu-ray
Blu-ray players are backward compatible with audio CD. By the early 2000s, the CD player
CD player had largely replaced the audio cassette player as standard equipment in new automobiles, with 2010 being the final model year for any car in the United States to have a factory-equipped cassette player.[40] With the increasing popularity of portable digital audio players, such as mobile phones, and solid state music storage, CD players are being phased out of automobiles in favor of minijack auxiliary inputs, wired connection to USB devices and wireless Bluetooth
Bluetooth connection.[41] Meanwhile, with the advent and popularity of Internet-based distribution of files in lossily-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%,[42] although independent and DIY music sales may be tracking better according to figures released 30 March 2009, and CDs still continue to sell greatly.[43] As of 2012, CDs and DVDs made up only 34 percent of music sales in the United States.[44] By 2015[update], only 24% of music in the United States was purchased on physical media, ⅔ of this consisting of CDs;[45] however, in the same year in Japan, over 80% of music was bought on CDs and other physical formats.[46] Despite the rapidly declining sales year-over-year, the pervasiveness of the technology remained for a time, with companies placing CDs in pharmacies, supermarkets, and filling station convenience stores targeting buyers least able to utilize Internet-based distribution.[11] However, in 2018, Best Buy
Best Buy announced plans to end CD sales in its stores on July 1, 2018, with Target Corporation
Target Corporation planning to only offer CDs on a consignment basis.[47] Awards and accolades[edit] Sony
Sony and Philips
Philips received praise for the development of the compact disc from professional organizations. These awards include

Technical Grammy Award
Grammy Award for Sony
Sony and Philips, 1998.[48] IEEE
IEEE Milestone award, 2009, for Philips
Philips only with the citation: "On 8 March 1979, N.V. Philips' Gloeilampenfabrieken demonstrated for the international press a Compact Disc Audio Player. The demonstration showed that it is possible by using digital optical recording and playback to reproduce audio signals with superb stereo quality. This research at Philips
Philips established the technical standard for digital optical recording systems."[49]

Physical details[edit]

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Diagram of CD layers.

A polycarbonate disc layer has the data encoded by using bumps. A shiny layer reflects the laser. A layer of lacquer protects the shiny layer. Artwork is screen printed on the top of the disc. A laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data

A CD is made from 1.2 millimetres (0.047 in) thick, polycarbonate plastic and weighs 15–20 grams.[50][better source needed] From the center outward, components are: the center spindle hole (15 mm), the first-transition area (clamping ring), the clamping area (stacking ring), the second-transition area (mirror band), the program (data) area, and the rim. The inner program area occupies a radius from 25 to 58 mm. A thin layer of aluminium or, more rarely, gold is applied to the surface, making it reflective. The metal is protected by a film of lacquer normally spin coated directly on the reflective layer. The label is printed on the lacquer layer, usually by screen printing or offset printing. CD data is represented as tiny indentations known as "pits", encoded in a spiral track moulded into the top of the polycarbonate layer. The areas between pits are known as "lands". Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 µm in length.[51] The distance between the tracks, the pitch, is 1.6 µm.[52][53][54] A motor within the CD player
CD player spins the disc to a scanning velocity of 1.2–1.4 m/s (constant linear velocity) – equivalent to approximately 500 RPM at the inside of the disc, and approximately 200 RPM at the outside edge. (A disc played from beginning to end slows its rotation rate during playback.)

Comparison of various optical storage media

The program area is 86.05 cm2 and the length of the recordable spiral is (86.05 cm2 / 1.6 µm) = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or 650 MiB of data on a CD-ROM. A disc with data packed slightly more densely is tolerated by most players (though some old ones fail). Using a linear velocity of 1.2 m/s and a narrower track pitch of 1.5 µm increases the playing time to 80 minutes, and data capacity to 700 MiB.

The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and 150 nm deep

A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser housed within the CD player, through the bottom of the polycarbonate layer. The change in height between pits and lands results in a difference in the way the light is reflected. By measuring the intensity change with a photodiode, the data can be read from the disc. In order to accommodate the spiral pattern of data, the semiconductor laser is placed on a swing arm within the disc tray of any CD player. This swing arm allows the laser to read information from the centre to the edge of a disc, without having to interrupt the spinning of the disc itself.

Philips
Philips CDM210 CD Drive

The pits and lands do not directly represent the zeros and ones of binary data. Instead, non-return-to-zero, inverted encoding is used: a change from pit to land or land to pit indicates a one, while no change indicates a series of zeros. There must be at least two and no more than ten zeros between each one, which is defined by the length of the pit. This in turn is decoded by reversing the eight-to-fourteen modulation used in mastering the disc, and then reversing the cross-interleaved Reed–Solomon coding, finally revealing the raw data stored on the disc. These encoding techniques (defined in the Red Book) were originally designed for CD Digital Audio, but they later became a standard for almost all CD formats (such as CD-ROM). Integrity[edit] CDs are susceptible to damage during handling and from environmental exposure. Pits are much closer to the label side of a disc, enabling defects and contaminants on the clear side to be out of focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic or by careful polishing. The edges of CDs are sometimes incompletely sealed, allowing gases and liquids to corrode the metal reflective layer and to interfere with the focus of the laser on the pits.[55] The fungus Geotrichum candidum
Geotrichum candidum has been found—under conditions of high heat and humidity—to consume the polycarbonate plastic and aluminium found in CDs.[56][57] Disc shapes and diameters[edit]

Comparison of several forms of disk storage showing tracks (not-to-scale); green denotes start and red denotes end. * Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.

The digital data on a CD begins at the center of the disc and proceeds toward the edge, which allows adaptation to the different size formats available. Standard CDs are available in two sizes. By far, the most common is 120 millimetres (4.7 in) in diameter, with a 74- or 80-minute audio capacity and a 650 or 700 MiB (737,280,000-byte) data capacity. This capacity was reportedly specified by Sony executive Norio Ohga in May 1980 so as to be able to contain the entirety of Beethoven's Ninth Symphony
Beethoven's Ninth Symphony on one disc.[23] This is a myth according to Kees Immink, as the code format had not yet been decided in May 1980.[10] The adoption of EFM one month later would have allowed a playing time of 97 minutes for 120 mm diameter or 74 minutes for a disc as small as 100 mm.[58] The 120 mm diameter has been adopted by subsequent formats, including Super Audio CD, DVD, HD DVD, and Blu-ray
Blu-ray Disc. The 80 mm diameter discs ("Mini CDs") can hold up to 24 minutes of music or 210 MiB.

Physical size Audio Capacity CD-ROM
CD-ROM Data Capacity Definition

120 mm 74–80 min 650–700 MiB Standard size

80 mm 21–24 min 185–210 MiB Mini-CD size

80x54 mm – 80x64 mm ~6 min 10-65 MiB "Business card" size

Logical format[edit] Audio CD[edit] Main article: Compact Disc Digital Audio The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced in 1980 by the format's joint creators, Sony
Sony and Philips. The document is known colloquially as the Red
Red Book CD-DA
CD-DA after the colour of its cover. The format is a two-channel 16-bit PCM encoding at a 44.1 kHz sampling rate per channel. Four-channel sound was to be an allowable option within the Red
Red Book format, but has never been implemented. Monaural
Monaural audio has no existing standard on a Red
Red Book CD; thus, mono source material is usually presented as two identical channels in a standard Red
Red Book stereo track (i.e., mirrored mono); an MP3
MP3 CD, however, can have audio file formats with mono sound. CD-Text
CD-Text is an extension of the Red
Red Book specification for audio CD that allows for storage of additional text information (e.g., album name, song name, artist) on a standards-compliant audio CD. The information is stored either in the lead-in area of the CD, where there is roughly five kilobytes of space available, or in the subcode channels R to W on the disc, which can store about 31 megabytes. Compact Disc + Graphics
Compact Disc + Graphics is a special audio compact disc that contains graphics data in addition to the audio data on the disc. The disc can be played on a regular audio CD player, but when played on a special CD+G
CD+G player, it can output a graphics signal (typically, the CD+G player is hooked up to a television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a television set for karaoke performers to sing along with. The CD+G
CD+G format takes advantage of the channels R through W. These six bits store the graphics information. CD + Extended Graphics (CD+EG, also known as CD+XG) is an improved variant of the Compact Disc + Graphics
Compact Disc + Graphics (CD+G) format. Like CD+G, CD+EG utilizes basic CD-ROM
CD-ROM features to display text and video information in addition to the music being played. This extra data is stored in subcode channels R-W. Very few, if any, CD+EG discs have been published. Super Audio CD[edit] Main article: Super Audio CD Super Audio CD
Super Audio CD (SACD) is a high-resolution read-only optical audio disc format that was designed to provide higher fidelity digital audio reproduction than the Red
Red Book. Introduced in 1999, it was developed by Sony
Sony and Philips, the same companies that created the Red
Red Book. SACD was in a format war with DVD-Audio, but neither has replaced audio CDs. The SACD standard is referred to the Scarlet Book standard. Titles in the SACD format can be issued as hybrid discs; these discs contain the SACD audio stream as well as a standard audio CD layer which is playable in standard CD players, thus making them backward compatible. CD-MIDI[edit] CD- MIDI
MIDI is a format used to store music-performance data, which upon playback is performed by electronic instruments that synthesize the audio. Hence, unlike the original Red
Red Book CD-DA, these recordings are not digitally sampled audio recordings. The CD- MIDI
MIDI format is defined as an extension of the original Red
Red Book. CD-ROM[edit] Main article: CD-ROM For the first few years of its existence, the CD was a medium used purely for audio. However, in 1988, the Yellow Book CD-ROM
CD-ROM standard was established by Sony
Sony and Philips, which defined a non-volatile optical data computer data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. Video CD
Video CD (VCD)[edit] Main article: Video CD Video CD
Video CD (VCD, View CD, and Compact Disc digital video) is a standard digital format for storing video media on a CD. VCDs are playable in dedicated VCD
VCD players, most modern DVD-Video
DVD-Video players, personal computers, and some video game consoles. The VCD
VCD standard was created in 1993 by Sony, Philips, Matsushita, and JVC
JVC and is referred to as the White Book standard. Overall picture quality is intended to be comparable to VHS
VHS video. Poorly compressed VCD
VCD video can sometimes be lower quality than VHS video, but VCD
VCD exhibits block artifacts rather than analog noise and does not deteriorate further with each use. 352x240 (or SIF) resolution was chosen because it is half the vertical and half the horizontal resolution of NTSC video. 352x288 is similarly one quarter PAL/SECAM resolution. This approximates the (overall) resolution of an analog VHS
VHS tape, which, although it has double the number of (vertical) scan lines, has a much lower horizontal resolution. Super Video CD[edit] Main article: Super Video CD Super Video CD
Video CD (Super Video Compact Disc or SVCD) is a format used for storing video media on standard compact discs. S VCD
VCD was intended as a successor to VCD
VCD and an alternative to DVD-Video
DVD-Video and falls somewhere between both in terms of technical capability and picture quality. S VCD
VCD has two thirds the resolution of DVD, and over 2.7 times the resolution of VCD. One CD-R
CD-R disc can hold up to 60 minutes of standard quality SVCD-format video. While no specific limit on S VCD
VCD video length is mandated by the specification, one must lower the video bit rate, and therefore quality, to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video onto one S VCD
VCD without incurring significant quality loss, and many hardware players are unable to play video with an instantaneous bit rate lower than 300 to 600 kilobits per second. Photo CD[edit] Main article: Photo CD Photo CD
Photo CD is a system designed by Kodak
Kodak for digitizing and storing photos on a CD. Launched in 1992, the discs were designed to hold nearly 100 high-quality images, scanned prints and slides using special proprietary encoding. Photo CDs are defined in the Beige Book and conform to the CD-ROM
CD-ROM XA and CD-i Bridge
CD-i Bridge specifications as well. They are intended to play on CD-i players, Photo CD
Photo CD players and any computer with suitable software (irrespective of operating system). The images can also be printed out on photographic paper with a special Kodak
Kodak machine. This format is not to be confused with Kodak Picture CD, which is a consumer product in CD-ROM
CD-ROM format. CD-i[edit] Main article: Philips
Philips CD-i The Philips
Philips Green Book specifies a standard for interactive multimedia compact discs designed for CD-i players (1993). CD-i discs can contain audio tracks which can be played on regular CD players, but CD-i discs are not compatible with most CD-ROM
CD-ROM drives and software. The CD-i Ready specification was later created to improve compatibility with audio CD players, and the CD-i Bridge
CD-i Bridge specification was added to create CD-i compatible discs that can be accessed by regular CD-ROM drives. CD-i Ready[edit] Main article: CD-i Ready Philips
Philips defined a format similar to CD-i called CD-i Ready, which puts CD-i software and data into the pregap of track 1. This format was supposed to be more compatible with older audio CD players. Enhanced Music CD
Enhanced Music CD (CD+)[edit] Main article: Blue Book (CD standard) Enhanced Music CD, also known as CD Extra or CD Plus, is a format which combines audio tracks and data tracks on the same disc by putting audio tracks in a first session and data in a second session. It was developed by Philips
Philips and Sony, and it is defined in the Blue Book. Vinyl Disc[edit] Main article: VinylDisc Vinyl Disc is the hybrid of a standard audio CD and the vinyl record. The vinyl layer on the disc's label side can hold approximately three minutes of music. Manufacture[edit] Main article: CD manufacturing

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Individual pits are visible on the micrometre scale

Replicated CDs are mass-produced initially using a hydraulic press. Small granules of heated raw polycarbonate plastic are fed into the press. A screw forces the liquefied plastic into the mold cavity. The mold closes with a metal stamper in contact with the disc surface. The plastic is allowed to cool and harden. Once opened, the disc substrate is removed from the mold by a robotic arm, and a 15 mm diameter center hole (called a stacking ring) is created. The time it takes to "stamp" one CD is usually two to three seconds.[citation needed] This method produces the clear plastic blank part of the disc. After a metallic reflecting layer (usually aluminium, but sometimes gold or other metal) is applied to the clear blank substrate, the disc goes under a UV light for curing and it is ready to go to press. To prepare to press a CD, a glass master is made, using a high-powered laser on a device similar to a CD writer. The glass master is a positive image of the desired CD surface (with the desired microscopic pits and lands). After testing, it is used to make a die by pressing it against a metal disc.[citation needed] The die is a negative image of the glass master: typically, several are made, depending on the number of pressing mills that are to make the CD. The die then goes into a press, and the physical image is transferred to the blank CD, leaving a final positive image on the disc. A small amount of lacquer is applied as a ring around the center of the disc, and rapid spinning spreads it evenly over the surface. Edge protection lacquer is applied before the disc is finished. The disc can then be printed and packed.[citation needed] Manufactured CDs that are sold in stores are sealed via a process called "polywrapping" or shrink wrapping.[citation needed] In 1995, material costs were 30 cents for the jewel case and 10 to 15 cents for the CD. Wholesale cost of CDs was $0.75 to $1.15, which retailed for $16.98.[59] On average, the store received 35 percent of the retail price, the record company 27 percent, the artist 16 percent, the manufacturer 13 percent, and the distributor 9 percent.[59] When 8-track tapes, cassette tapes, and CDs were introduced, each was marketed at a higher price than the format they succeeded, even though the cost to produce the media was reduced. This was done because the apparent value increased. This continued from vinyl to CDs but was broken when Apple marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3
MP3 is very small.[60] Writable compact discs[edit] Recordable CD[edit]

700 MiB CD-R
CD-R next to a mechanical pencil

Main article: CD-R Recordable Compact Discs, CD-Rs, are injection-molded with a "blank" data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the CD recorder changes the colour of the dye to allow the read laser of a standard CD player
CD player to see the data, just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM
CD-ROM drives and played in most audio CD players. CD-Rs follow the Orange Book standard. CD-R
CD-R recordings are designed to be permanent. Over time, the dye's physical characteristics may change causing read errors and data loss until the reading device cannot recover with error correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions. However, testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions.[61][62] This failure is known as disc rot, for which there are several, mostly environmental, reasons.[63] The recordable audio CD is designed to be used in a consumer audio CD recorder. These consumer audio CD recorders use SCMS (Serial Copy Management System), an early form of digital rights management (DRM), to conform to the AHRA (Audio Home Recording Act). The Recordable Audio CD is typically somewhat more expensive than CD-R
CD-R due to lower production volume and a 3% AHRA royalty used to compensate the music industry for the making of a copy.[64] High-capacity recordable CD is a higher-density recording format that can hold 90 or 99 minutes of audio on a 12 cm (5 in) disc (compared to about 80 minutes for Red
Red Book audio) or 30 minutes of audio on an 8 cm (3 in) disc (compared to about 24 minutes for Red
Red Book audio).[65] The higher capacity is incompatible with some recorders and recording software.[66] ReWritable CD[edit] Main article: CD-RW CD-RW
CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the properties (amorphous vs. crystalline) of the alloy, and hence change its reflectivity. A CD-RW
CD-RW does not have as great a difference in reflectivity as a pressed CD or a CD-R, and so many earlier CD audio players cannot read CD-RW
CD-RW discs, although most later CD audio players and stand-alone DVD
DVD players can. CD-RWs follow the Orange Book standard. The ReWritable Audio CD is designed to be used in a consumer audio CD recorder, which will not (without modification) accept standard CD-RW discs. These consumer audio CD recorders use the Serial Copy Management System (SCMS), an early form of digital rights management (DRM), to conform to the United States' Audio Home Recording Act (AHRA). The ReWritable Audio CD is typically somewhat more expensive than CD-RW
CD-RW due to (a) lower volume and (b) a 3% AHRA royalty used to compensate the music industry for the making of a copy.[64] Speed[edit] Due to technical limitations, the original ReWritable CD could be written no faster than 4x speed. High Speed ReWritable CD has a different design, which permits writing at speeds ranging from 4x to 12x. Original CD-RW
CD-RW drives can only write to original ReWritable CDs. High Speed CD-RW
CD-RW drives can typically write to both original ReWritable CDs and High Speed ReWritable CDs. Both types of CD-RW discs can be read in most CD drives. Higher speed CD-RW
CD-RW discs, Ultra Speed (16x to 24x write speed) and Ultra Speed+ (32x write speed) are now available. Copy protection[edit] Main article: CD/ DVD
DVD copy protection The Red
Red Book audio specification, except for a simple "anti-copy" statement in the subcode, does not include any copy protection mechanism. Known at least as early as 2001,[67] attempts were made by record companies to market "copy-protected" non-standard compact discs, which cannot be ripped, or copied, to hard drives or easily converted to other formats (like FLAC, MP3
MP3 or Vorbis). One major drawback to these copy-protected discs is that most will not play on either computer CD-ROM
CD-ROM drives or some standalone CD players that use CD-ROM
CD-ROM mechanisms. Philips
Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio
Compact Disc Digital Audio logo because they violate the Red
Red Book specifications. Numerous copy-protection systems have been countered by readily available, often free, software, or even by simply turning off automatic AutoPlay to prevent the running of the DRM executable program. See also[edit]

5.1 Music Disc Compact Disc bronzing Digipak DualDisc Extended Resolution Compact Disc High Definition Compatible Digital K2 High Definition Longbox SPARS code Video Single Disc

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